1. Field of the Invention
The present invention relates to an electromagnetic controlled fuel injector applied to an electromagnetic controlled unit injector, etc. for diesel engine and composed such that fuel injection timing thereof is controlled by means of a poppet valve which is reciprocated by a solenoid device to open or close the passage between the fuel passage to the plunger room where fuel is received and compressed to high pressure and the spill passage to the fuel return line.
2. Description of the Related Art
An electromagnetic controlled unit injector applied to a diesel engine is composed such that fuel injection timing is controlled through shutting-off/allowing communication of a fuel passage, which connects to a plunger room where fuel is introduced and compressed to high pressure, with a spill passage connecting to a fuel return line by closing/opening a poppet valve reciprocated by means of a solenoid device. In order to improve operation stability at low load and to improve performance of output and fuel consumption, it is imperative that closing response of the poppet valve is good and injection cutoff is sharp.
There are such means as increase force for driving the poppet valve, that is, increase attraction force of the solenoid device and spring force of the poppet valve spring to increase opening/closing velocity of the poppet valve or decrease the size of the poppet valve to increase opening/closing velocity of the poppet valve in order to quicken opening/closing response of the poppet valve of the electromagnetic controlled unit injector. Opening/closing response of a poppet valve can be improved by these means.
However, in the case of increasing attraction force of the solenoid device, there is a problem that the size of the solenoid device increases.
FIGS. 4(A) and 4(B) are sectional views of the substantial part of the solenoid device and poppet valve device of an electromagnetic controlled unit injector for explaining downsizing of the poppet valve. In FIGS. 4(A) and 4(B), reference numeral 6 is a solenoid device, 6a is an electromagnetic coil of the solenoid device 6, 01 is a poppet valve reciprocated by the actuation of the solenoid device, 2 is a valve seal member having a seat part for allowing a seat part 4 of the poppet valve 01 to seat thereon, 5 is an armature which is fixed to the upper end of the poppet valve 01, a gap being provided between the armature 5 and the electromagnetic coil 6a. 
In the electromagnetic controlled unit injector provided with the electromagnetic open/close valve device as shown in FIG.4(B), when the solenoid device is not excited, said gap between the armature 5 and the electromagnetic coil 6a is C2, and there is a valve seat passage 15 between the seat part of the poppet valve 01 and valve seat member 2.
Therefore, a plunger room not shown in the drawing is communicated to a spill passage 3 through a fuel passage 2b, a fuel pool 2a in the valve seat member 2, and the valve seat passage 15.
When the solenoid device 6 is excited, the armature 5 is attracted by the electromagnetic coil 6a of the solenoid device 6 to move the poppet valve 01 upward to allow the seat part 4 of the poppet valve 01 to contact with the seat part of the valve seat member, and the valve seat passage 15 is closed. Therefore, the fuel in the plunger room can be compressed to high pressure.
If the diameter d0 of the poppet valve 01 is decreased, the closing speed thereof is increased when the attraction force is the same, resulting in a quicker valve closing response, which improves operation stability at low engine load.
In JP7-269438A discloses a passage open/close valve device, in which the valve opening stroke is allowed to be long with the valve closing stroke being restricted to be short, and rapid pressure drop at the injection end is effected by the increased valve opening stroke resulting in sharpened injection cutoff.
WO 02/04805 discloses a fuel injection device, in which a main and a sub electromagnetic valve are provided, and injection rate is controlled by the effect of an orifice provided to the line provided with the sub electromagnetic valve.
In the conventional electromagnetic unit injector equipped with the electromagnetic opening/closing valve device of FIG. 4, when the diameter d0 of the poppet valve 01 shown in FIG. 4(A) is decreased to d2 as shown in FIG. 4(B) in order to quicken valve closing response at the beginning, it is necessary to increase the stroke of the poppet valve 01 from L1 in FIG. 4(A) to L2 in FIG. 4(B), for the area of the valve seat passage 15 when the poppet valve 01 is opened must be large enough in order not to deteriorate injection cutoff at the injection end.
However, when the stroke of the poppet valve 01 is increased, the gap between the electromagnetic coil 6a of the solenoid device 6 and the armature fixed to the poppet valve 01 must be increased by ΔC from C1 in FIG.4(A) to C2 in FIG.4(B), so closing response of the poppet valve 01 becomes slower and operation stability at low load operation of the engine is deteriorated.
According to said JP7-269438A, the opening stroke of the poppet valve can be increased to effect rapid pressure drop at the injection end in order to sharpen injection cutoff with the closing stroke by keeping short. However, in the device of the conventional art, high liquid pressure when the valve is seating exerts on members for switching valve lift, and the construction including the valve spool, stopper sleeve, springs, etc. is complicated, the number of constituent parts increases, and man-hour for manufacturing and assembling increase resulting in increased cost.
The fuel injection device disclosed in WO 02/04805 controls the transition mode of fuel injection pressure through controlling the flow of fuel return by providing variable opening orifice, not controls the stroke of the poppet valve.